Certain applications require analog/digital converters exhibiting a high sampling frequency and high resolution. Among these applications are cable TV transmissions, optical communications, and satellite communications in which one or more modulated signals are transmitted simultaneously on a wide frequency band (for example several GHz wide).
Moreover the use of ever more complex modulations requires digitization of the signals on a large number of bits.
Architectures with a single converter struggle to satisfy the performance demanded at an acceptable cost in terms of consumption and surface area.
Hence, to make it possible to meet this need, structures with several analog/digital converters said to be “temporally interleaved” (TIADCs: Time-Interleaved Analog-to-Digital Converters) have established themselves. In such a time-interleaved structure the temporally interleaved analog/digital converters respectively perform temporally shifted analog/digital conversions of an analog signal. Stated otherwise, if the structure comprises M converters, the latter successively sample each in their turn the signal at a frequency equal to Fs/M, where Fs is the global frequency of sampling of the structure.
However the drawback of this type of structure resides in the fact that mismatches (“mispairings”), even slight ones, between the converters create spurious spectral lines or frequency bands that may be situated in the frequency zone of the useful signal. And in the case, for example, of television signals containing several channels, these spurious spectral lines or bands can disturb some of these channels.
These mismatches can have various causes, such as for example clock shifts (“timing skew”) and possibly gains and/or shifts (“offset”), that differ between the converters of the structure.
A mismatch in terms of clock shift or gain adds to the frequency spectrum of the output signal attenuated spurious images of the frequency spectrum of the input signal around the frequencies that are multiples of Fs/M.
A mismatch in terms of shift (“offset”) creates spurious spectral lines localized at frequencies that are multiples of Fs/M. Furthermore these shifts can vary over time.